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lammps/src/random_mars.cpp
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random_mars.cpp
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/* ----------------------------------------------------------------------
LAMMPS - Large-scale Atomic/Molecular Massively Parallel Simulator
http://lammps.sandia.gov, Sandia National Laboratories
Steve Plimpton, sjplimp@sandia.gov
Copyright (2003) Sandia Corporation. Under the terms of Contract
DE-AC04-94AL85000 with Sandia Corporation, the U.S. Government retains
certain rights in this software. This software is distributed under
the GNU General Public License.
See the README file in the top-level LAMMPS directory.
------------------------------------------------------------------------- */
// Marsaglia random number generator
#include "math.h"
#include "random_mars.h"
#include "error.h"
using namespace LAMMPS_NS;
/* ---------------------------------------------------------------------- */
RanMars::RanMars(LAMMPS *lmp, int seed) : Pointers(lmp)
{
int ij,kl,i,j,k,l,ii,jj,m;
double s,t;
if (seed <= 0 || seed > 900000000)
error->all("Invalid seed for Marsaglia random # generator");
save = 0;
u = new double[97+1];
ij = (seed-1)/30082;
kl = (seed-1) - 30082*ij;
i = (ij/177) % 177 + 2;
j = ij %177 + 2;
k = (kl/169) % 178 + 1;
l = kl % 169;
for (ii = 1; ii <= 97; ii++) {
s = 0.0;
t = 0.5;
for (jj = 1; jj <= 24; jj++) {
m = ((i*j) % 179)*k % 179;
i = j;
j = k;
k = m;
l = (53*l+1) % 169;
if ((l*m) % 64 >= 32) s = s + t;
t = 0.5*t;
}
u[ii] = s;
}
c = 362436.0 / 16777216.0;
cd = 7654321.0 / 16777216.0;
cm = 16777213.0 / 16777216.0;
i97 = 97;
j97 = 33;
uniform();
}
/* ---------------------------------------------------------------------- */
RanMars::~RanMars()
{
delete [] u;
}
/* ----------------------------------------------------------------------
uniform RN
------------------------------------------------------------------------- */
double RanMars::uniform()
{
double uni = u[i97] - u[j97];
if (uni < 0.0) uni += 1.0;
u[i97] = uni;
i97--;
if (i97 == 0) i97 = 97;
j97--;
if (j97 == 0) j97 = 97;
c -= cd;
if (c < 0.0) c += cm;
uni -= c;
if (uni < 0.0) uni += 1.0;
return uni;
}
/* ----------------------------------------------------------------------
gaussian RN
------------------------------------------------------------------------- */
double RanMars::gaussian()
{
double first,v1,v2,rsq,fac;
if (!save) {
int again = 1;
while (again) {
v1 = 2.0*uniform()-1.0;
v2 = 2.0*uniform()-1.0;
rsq = v1*v1 + v2*v2;
if (rsq < 1.0 && rsq != 0.0) again = 0;
}
fac = sqrt(-2.0*log(rsq)/rsq);
second = v1*fac;
first = v2*fac;
save = 1;
} else {
first = second;
save = 0;
}
return first;
}
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